Author Archive

… but instead, we’re swamped with a combination of SPIRE-related technical work, miscellaneous activities for our home institute (such as teaching, and the list goes on) and bottom of the pile, finding time to do some actual science. The various science teams are retrenching/reorganising to produce new papers/results now that the hectic Science Demonstration paper era has now passed – so expect to see a whole new slew of results over the next few months on here.

ESA held a press conference a couple of hours ago to highlight some of the results from the ESLAB meeting. If you missed the live stream earlier, you can catch it here .

A number of major programs released some mouth-watering data to the general public, ranging from high resolution studies of massive star formation in our own Galaxy (the massive bubble RCW 120, which contains an embryonic massive Wolf-Rayet star, and huge star forming complexes in Aquila and Vulpecula) to studies of the high redshift universe (the H-ATLAS program).

Credits: ESA/ATLAS Consortium

A picture of the first field observed in the H-ATLAS survey, made by combining the images made with the SPIRE camera at 250, 350 and 500 microns. The colours in the image are not real but have been used to represent the different infrared wavelengths. The faint blue whisps at the top of the image show dust in our own Galaxy and the bright object just above the centre of the picture is a ‘Bok globule’, a dense cloud of gas and dust, also in our Galaxy, in which a small star may be forming. The other objects in the picture are all galaxies, at distances up to 12 billion light-years. The image shows that the survey is detecting objects in our celestial ‘backyard’ and also other, further ones that we are seeing as they were not long after the Big Bang.

Credits: ESA/Hi-GAL Consortium

This image, in the constellation of Vulpecula, shows an entire assembly line of newborn stars. The diffuse glow reveals the widespread cold reservoir of raw material that our Galaxy has in stock for building stars.

Large-scale turbulence from the giant colliding Galactic flows causes this material to condense into the web of filaments that we see all over the image. These are the ‘pregnant’ entities where the material becomes colder and denser. At this point, gravitational forces take over and fragment these filaments into chains of stellar embryos that can finally collapse to form baby stars.

Credits: ESA/Hi-GAL Consortium

At the centre and the left of the image, the two massive star-forming regions G29.9 and W43 are clearly visible. These mini-starbursts are forming, as we speak, hundreds and hundreds of stars of all sizes: from those similar to our Sun, to monsters several tens of times heavier than our Sun.

These newborn large stars are catastrophically disrupting their original gas embryos by kicking away their surroundings and excavating giant cavities in the Galaxy. This is clearly visible in the ‘fluffy chimney’ below W43.

Credits: ESA/PACS/SPIRE/HOBYS Consortia

RCW 120 is a galactic bubble with a large surprise. How large? At least 8 times the mass of the Sun. Nestled in the shell around this large bubble is an embryonic star that looks set to turn into one of the brightest stars in the Galaxy.

The Galactic bubble is known as RCW 120. It lies about 4300 light-years away and has been formed by a star at its centre. The star is not visible at these infrared wavelengths but pushes on the surrounding dust and gas with nothing more than the power of its starlight. In the 2.5 million years the star has existed. It has raised the density of matter in the bubble wall so much that the quantity trapped there can now collapse to form new stars.

The bright knot to the right of the base of the bubble is an unexpectedly large, embryonic star, triggered into formation by the power of the central star. Herschel’s observations have shown that it already contains between 8-10 times the mass of our Sun. The star can only get bigger because it is surrounded by a cloud containing an additional 2000 solar masses.

Not all of that will fall onto the star, even the largest stars in the Galaxy do not exceed 150 solar masses. But the question of what stops the matter falling onto the star is a puzzle for modern astronomers. According to theory, stars should stop forming at about 8 solar masses. At that mass they should become so hot that they shine powerfully at ultraviolet wavelengths.

This light should push the surrounding matter away, much as the central star did to form this bubble. But clearly sometimes this mass limit is exceeded otherwise there would be no giant stars in the Galaxy. So astronomers would like to know how some stars can seem to defy physics and grow so large. Is this newly discovered stellar embryo destined to grow into a stellar monster? At the moment, nobody knows but further analysis of this Herschel image could give us invaluable clues.

The press release (which this post is based upon quite heavily!), and high-res JPEGS of these images can be found at the ESA Herschel web site.

Additional First Science press releases – which we’ll return to later – can also be found here.

The first results on an extragalactic object here at ESLAB were presented this afternoon on the HERITAGE survey of the Large Magellanic Cloud – a follow-up program to a major Spitzer program to study the effects of star formation on the surrounding gas and dust in an environment that differs quite significantly from our own Galactic neighbourhood at high spatial resolution.

The HERITAGE team presented results from a central strip through the LMC that was observed as part of the Science Demonstration phase – one of the central results to emerge from this is the need for refinement of standard dust models when applied to environments such as the LMC. The harsh radiation environment, plus comparative lack of dust in the LMC leaves traditional dust models predicted too much dust – a different approach, based on modelling with amorphous carbon seems allow better constraints on the overall spectral energy distribution, especially as we move to longer wavelengths – too much dust can lead to an over-estimate of the amount of very, very cold dust (temperatures ~ 5-10 K!). There’s also tantalising hints of an over-abundance of polycyclic aromatic hydrocarbons (PAHs – basically soot, or the stuff burnt on an overdone hamburger) co-incident with the stellar bar in the LMC – for more details, sadly, I’ll have to talk to the presenter…

Some excellent news to report – the HIFI instrument on Herschel (the high resolution spectrometer) has been successfully switched on after lying dormant for 4 months, after suffering an unwanted voltage peak in the electronic system of HIFI, which in August led to a faulty diode in a DC/DC convertor.

After several months of troubleshooting and the development of a new operating procedure to prevent a similar occurence, HIFI was commanded to switch on using its redundant electronics chain on Sunday, followed by an upload of revised software and a “Short Functional Test” – a complete HIFI health check. All were carried out successfully.

The next step in HIFI’s rehab comes in the new year – the instrument was only starting its performance verification effort, so an an intense post-Christmas re-commissioning and calibration campaign is required to bring HIFI back up to speed and ready to use for regular observing as per SPIRE and PACS.

At 00hrs UT, Herschel was 1.415 million kilometres from Earth and receding at 192m/s (691km/h). Signals now take 4.5s to reach it. In terms of position in the sky, it is about 6 degrees north of the magnitude 4.6 star, 20 Ophiuchi.

Herschel is in good shape, with its cooler reaching a temperature of 287mK when it is re-cycled. It will get even colder as we approach operational temperature. The next big event is the cryostat lid in a few days – the Herschel UK outreach site gives a nice overview of the timelines for commissioning phase, plus a nice video of the lid release mechanism at work.

The first interferogram the the SPIRE SMEC Fourier Transform Spectrometer. Although it is of the cryostat lid, it shows how well the SPIRE spectrometer is performing in its first tests in space. Exciting stuff!

Herschel is now over 1.2 million km from Earth and receding at 0.32km/s. Signals now take 4.0 seconds to reach the spacecraft. The spacecraft – from the point of view of an observer on Earth – is located in the constellation of Ophiuchus, and was imaged last night by Peter Birtwhistle (West Berkshire, UK) using a 16″ Meade Schmitt-Cassegrain and by the Catalina Sky Survey at a visual magnitude of 17.8. Amazing stuff that amateur (especially) astronomers can routinely image such faint objects, alongside their professional counterparts! Well done to both.

‘First light’ – after we have removed the cryocover and when we observe our first object – is scheduled for June 14th, so busy (and scary) times lie ahead of us! PACS testing seems to have gone well too – congrats to the PACS team!